Numerous arrangements have been studied and developed to convert thermal energy into mechanical energy for performing work. Most such arrangements operate indirectly to perform such an energy conversion. For example, one conventional technique is to generate steam with solar or some other form of thermal energy and to direct the steam through a turbine to generate rotary shaft power. A number of alternatives have been studied which also involve heating an appropriate medium to, in turn, thermodynamically or mechanically drive various devices such as piston, rankine and stirling engines. Such methods also involve an indirect conversion of energy.
Two methods of directly converting thermal energy to mechanical energy come to mind. The familiar bimetallic strip used in thermostats operates on the principle of differing coefficients of heat expansion of two bonded strips of metal. A spiral coil of such a bimetallic strip either contracts or expands as the ambient temperature changes. The bimetallic strip does not appear to be useful for generating significant amounts of mechanical energy. One reason for this is the complex linkages that would be required to convert the mechanical movement of such a strip to rotary shaft power. A more important reason is the fact that the bimetallic is not conveniently capable of generating continuous mechanical energy.
A second direct conversion method mentioned above concerns the well known pinwheel device most commonly used as a demonstration oddity. One surface of each vane of the pinwheel is dark and the opposite surface is reflective. The dark surfaces absorb more heat than the reflective surfaces. Illuminating the pinwheel causes it to rotate by means of a reactive force resulting from the expanding air adjacent the hotter dark vane surfaces. While this arrangement is capable of continuously generating rotational energy, it appears that no attempt has been made to utilize it for applications requiring significant amounts of power.
Thus, an arrangement for practical application and capable of continuously and directly converting thermal energy into shaft power of significant amounts is desirable.